Diabetes is a common metabolic disease. It is characterized by abnormally high plasma glucose concentration showed in the fasting state or during the oral glucose tolerance test and hyperglycemia. The World Health Organization divides diabetes into type 1 and type 2 according to the clinical forms, and most diabetes patients suffer from type 2 diabetes mellitus (T2DM). Type 2 diabetes mellitus, also known as non-insulin dependent diabetes mellitus, is accompanied by high vascular complications, such as coronary artery disease, stroke, high blood pressure, kidney disease, peripheral vascular disease, neurological disease and retinopathy. This metabolic disorder has become a public health problem. There are nearly 194 million diabetics in the world according to a survey from World Health Organization and will be increased to 366 million by 2030. Promoting insulin secretion from pancreatic β-cells is the primary means for treating T2DM, however, in addition to therapeutic effects, there would be some side effects, such as: low blood sugar, weight gain, cardiovascular morbid reaction and β-cell death and the like.
Studies have shown that the complications in T2DM patients will decrease by 35%, when glycosylated hemoglobin Alc (HbAlc) decreases by 1%. Therefore, how to reduce complications and adverse side effects has been a major theme for treating type 2 diabetes. The targets for treating diabetes validated clinically include peroxisome proliferators-activated receptors (PPAR)α/γ, glucagon like peptidase-1 (GLP-1), dipeptidyl peptidase IV (DPPIV, DPP4) and the like. The DPPIV inhibitors have been a new choice for treating type 2 diabetes, and are relatively safe and effective medicaments so far whether administered alone or in combination.
Dipeptidyl peptidase IV (DPPIV; also known as T-cell antigen CD26), is a serine protease with high specificity in the form of dimer. It contains two states, one of which is transmembrane protease, comprising 766 amino acids, widely distributed in the kidney, intestine villus-like wall, cell membrane, hepatocytes, vascular endothelium, T cells, B cells, and NK cells. The other exists in the plasma in the form of dissolved state. The most important enzyme action for DPPIV is hydrolyzing polypeptides which contain alanine or prolinechain in N-terminal of the peptide chain, such as hydrolyzing GLP-1. If the activities of DPPIV can be inhibited, the content of GLP-1 in vivo can be improved indirectly which can induce a series of physiological actions in vivo and achieve the purpose of the treatment of type 2 diabetes.
Currently, the most widely used medicaments in clinic are anti-type 2 diabetes medicaments associated with GLP-1, such as (a) GLP-1 analogues resistant to DPPIV; (2) small molecule GLP-1 receptor agonists; and (c) DPPIV inhibitors. As a new oral antidiabetic agent, DPPIV inhibitor can prevent the rapid degradation of incretin hormone and improve the postprandial GLP-1 level with little side effects and good effects. The recent studies have shown that DPPIV inhibitors can reduce the level of glycosylated hemoglobin Alc whether administered alone or in combination with other antidiabetic agents. Also, the risk of hypoglycemia is small so that DPPIV inhibitors have already attracted more and more attention from pharmaceutical firms.
The studies on DPPIV inhibitors have already made a great breakthrough. Now the medicaments in the market include sitagliptin from Merck, vildagliptin from Novartis, saxagliptin from Bristol-Myers Squibb, alogliptin from Takeda, linagliptin from Boehringer Ingelheim and the like. Since the serine proteinase also has other families, their selectivity problems should be firstly considered and other side effects should be avoided. Therefore, the study on the DPPIV inhibitors still has a great challenge.